Clinical And Genetic Analysis Of Chinese Patients With Pseudohypoparathyroidism

Clinical and genetic analysis of Chinese patients with PseudohypoparathyroidismBackground:Pseudohypoparathyroidism (PHP) refers to a heterogeneous group of metabolic bone disorders characterized by resistance to the action of PTH. The two main subtype of PHP, PHP type 1a and 1b are caused by molecular defects within or upstream of the GNAS locus. Patients with PHP-1a, which due to inactivation mutation in GNAS gene, show Albright hereditary osteodystrophy (AHO) and resistance toward PTH and additional hormones. Whereas patients with PHP-1b, which due to methylation defects in four GNAS DMRs, do not have AHO and hormone resistance appears to limited to PTH and TSH. Recently, methylation defects have been detected in few patients with PHP and mild AHO, indicating an overlap between the two subtypes. Extensive exploration on the molecular level about the PHP patients have been conducted in many institutes worldwide, but the research regarding Chinese patients is lacking.Objective:The aim of this study was to investigate the clinical and genetic characteristics in Chinese PHP patients, and provide further insight for the management of patients with this disease.Subjects and methods:Seventy-seven patients with clinically diagnosed PHP from PUMCH were recruited for this study. Clinical manifestations were retrospectively analysized. Methylation profile was characterised at the four GNAS DMRs through combined bisulfite restriction analysis and large fragment deletion in STX16 gene was identified by both long-range PCR and multiplex PCR. Inactivating mutations in GNAS gene were assessed by direct sequencing of PCR products. Results:A principal methylation analysis using COBRA at four GNAS DMRs provided three clusters of subjects including 17 PHP-la patients with normal methylation,13 AD-PHP-â… b patients with loss of methylation restricted to the A/B DMR, and 47 sporadic PHP-â… b patients with broad GNAS methylation changes. Furthermore,3.0 kb deletion in STX16 were identified in 9 patients. GNAS gene analysis identified three new mutations (c.314-316 del AAG, ins T c.352 insC, VS12+1G>T),and three mutations which have been previously described (c.103C>T, c.565-568 delGACT, c.1174G>A). Both PHP-1b familial patients and PHP-1b sporadic patients have, to certain extent, AHO phenotype and hypothyroidism, and there is no statistics differences between the two group. The disease severity is more prominent in PHP-1a patients than in PHP-1b patients regarding the AHO phenotype and TSH resistance.Conclusion:This is the largest research concerning clinical and genetic characterastics in Chinese PHP patients. Our findings provide further evidence that an overlap can exist between the clinical features of different PHP subtypes, and highlight the importance of a careful molecular and epigenetic analysis of GNAS for establishing the correct diagnosis and, thereby, providing appropriate clinical intervention and genetic counselling.